1. Field of the Invention
The present invention relates to an apparatus for obtaining information relating to a velocity at which a pulse wave propagates in a living subject, and an apparatus for measuring a blood-pressure index of a living subject.
2. Related Art Statement
Arteriosclerotic cardiovascular disease is one of major death causes of aged women, e.g., not younger than sixty five years, but there is no general method of finding latent arteriosclerosis. However, it is known that since measuring superior-and-inferior-limb blood-pressure index can be used as a simple and repeatable method to find inferior-limb arterial disease and can be used to check quickly and easily the condition of whole cardiovascular system, the index is useful to identify individuals who need special treatments to reduce its death rate or its incidence rate.
Generally, the above superior-and-inferior-limb blood-pressure index (hereinafter, abbreviated to the xe2x80x9cSIL BP indexxe2x80x9d) is obtained or calculated as the ratio of a systolic blood pressure (xe2x80x9cBPxe2x80x9d) of an ankle as the inferior-limb BP to a systolic blood pressure of an upper arm as the superior-limb BP, that is, ankle/arm BP index (abbreviated to xe2x80x9cAAIxe2x80x9d, xe2x80x9cAPIxe2x80x9d, or xe2x80x9cABIxe2x80x9d). If the measured ankle/arm blood pressure index of a living person is smaller than a threshold, e.g., about 0.9, abnormality may be diagnosed on the person.
As explained above, the SIL BP index, represented by the ankle/arm BP index, is used to find the inferior-limb arterial disease. However, even if a living person suffers the disease, the SIL BP index measured from the person may indicate a normal value. For example, in the case where a person has stenosis on a distal side of an abdominal artery but suffers arteriosclerosis in not only inferior limbs but also whole body, the SIL BP index measured from the person will indicate a normal value.
It is therefore an object of the present invention to provide a superior-and-inferior-limb blood-pressure (xe2x80x9cSIL BPxe2x80x9d) index measuring apparatus which assures that, in the case where the SIL BP index measured from a person indicates a normal value, a medical staff such as a doctor or a nurse can judge whether the normal SIL BP index value has resulted from the arteriosclerosis of the whole body of the person.
The Inventor has made various studies and found that, in the case where the SIL BP index is measured together with pulse-wave-propagation-velocity relating information which is known as an index which can be used to evaluate the degree of arteriosclerosis of the whole body of a person, a medical staff can judge whether a normal SIL BP index value measured from the person has resulted from the arteriosclerosis of the whole body of the person. The present invention has been developed based on this finding. As far as the present invention is concerned, the term xe2x80x9cpulse-wave-propagation-velocity-relating informationxe2x80x9d is defined as including pulse-wave-propagation velocity information which is obtained as pulse-wave propagation velocity itself or pulse-wave propagation time, and corrected pulse-wave-propagation-velocity information which is obtained by correcting the pulse-wave-propagation-velocity information to correspond to a reference BP value.
(1) According to a first feature of the present invention, there is provided an apparatus for measuring a superior-and-inferior-limb blood-pressure index of a living subject, comprising a first blood-pressure measuring device which measures a first blood pressure of an inferior limb of the subject; a second blood-pressure measuring device which measures a second blood pressure of a superior limb of the subject; index determining means for determining the superior-and-inferior-limb blood-pressure index, based on the first blood pressure measured by the first blood-pressure measuring device and the second blood pressure measured by the second blood-pressure measuring device; an information obtaining device which obtains propagation-velocity-relating information relating to a velocity of propagation of a pulse wave which propagates between two different portions of the subject; and a display device which simultaneously displays the superior-and-inferior-limb blood-pressure index determined by the index determining means and the propagation-velocity-relating information obtained by the information obtaining device. The phrase xe2x80x9csimultaneously displays the SIL BP index and the propagation-velocity-relating (xe2x80x9cPVRxe2x80x9d) information means that a time duration of displaying of the SIL BP index at least partly overlaps a time duration of displaying of the PVR information.
According to this feature, the index determining means determines an SIL BP index value based on the first BP value measured by the first BP measuring device and the second BP value measured by the second BP measuring device, and the information obtaining device obtains PVR information relating to the velocity of propagation of pulse wave which propagates between two different portions of the subject. In addition, the display device simultaneously displays the SIL index value determined by the index determining means and the PVR information obtained by the information obtaining device. Therefore, even if the thus determined SIL index value is normal, a medical staff can judge that the normal SIL index value has resulted from the arteriosclerosis of the whole body of the person, if the obtained PVR information is abnormal.
(2) According to a second feature of the present invention that includes the first feature (1), the apparatus further comprises an identifying device which identifies each one of a plurality of living subjects from the other living subjects; and a storing device which stores, for the each one living subject identified by the identifying device, at least one first superior-and-inferior-limb blood-pressure index value determined by the index determining means and at least one first propagation-velocity-relating information obtained by the information obtaining device, and the display device displays, for the each one living subject, the first superior-and-inferior-limb blood-pressure index value and the first propagation-velocity-relating information which are stored in the storing device, and a second superior-and-inferior-limb blood-pressure index value currently determined by the index determining means and a second propagation-velocity-relating information currently obtained by the information obtaining device, so that an observer can compare the first and second superior-and-inferior-limb blood-pressure index values with each other and compare the first and second propagation-velocity-relating information with each other. According to this feature, the display device displays, for each one living subject, the first SIL BP index value and PVR information stored in the storing device, and the second SIL BP index value currently determined by the index determining means and a second PVR information currently obtained by the information obtaining device, so that an observer can compare the first and second SIL BP index values with each other and compare the first and second PVR information with each other. Thus, the medical staff can easily recognize the respective degrees of advancement of the inferior-limb arteriostenosis and the general arteriosclerosis.
(3) According to a third feature of the present invention that includes the first or second feature (1) or (2), the display device comprises simultaneously displaying means for displaying, in a two-dimensional plane which is defined by a first axis representing superior-and-inferior-limb blood-pressure index and a second axis representing propagation-velocity relating information, a symbol at a position corresponding to the superior-and-inferior-limb blood-pressure index determined by the index determining means and the propagation-velocity relating information obtained by the information obtaining device. According to this feature, the medical staff can evaluate, in one glance, the determined SIL BP index value and the obtained PVR information.
(4) According to a fourth feature of the present invention that includes the second or third feature (2) or (3), the display device comprises timewise-change displaying means for displaying, in a two-dimensional plane which is defined by a first axis representing superior-and-inferior-limb blood-pressure index and a second axis representing propagation-velocity relating information, at least one first symbol at at least one position corresponding to the at least one first superior-and inferior-limb blood-pressure index value and the at least one first propagation-velocity-relating information which are stored in the storing device, and a second symbol at a position corresponding to the second superior-and-inferior-limb blood-pressure index value currently determined by the index determining means and the second propagation-velocity-relating information currently obtained by the information obtaining device. According to this feature, the medical staff can easily recognize, in one glance, the respective degrees of advancement of the inferior-limb arteriostenosis and the general arteriosclerosis.
(5) According to a fifth feature of the present invention that includes any one of the first to fourth features (1) to (4), the index determining means comprises means for determining, as the superior-and-inferior-limb blood-pressure index, a ratio of the first blood pressure to the second blood pressure, or a ratio of the second blood pressure to the first blood pressure.
(6) According to a sixth feature of the present invention that includes any one of the first to fifth features (1) to (5), the information obtaining device comprises two pulse-wave sensors which are worn on the two different portions of the living subject, respectively, and each of which detects the pulse wave at a corresponding one of the two portions.
(7) According to a seventh feature of the present invention that includes any one of the second to sixth features (2) to (6), the identifying device comprises an input device which is operable by an operator for inputting a batch of identification information identifying the each one living subject from the other living subjects; a memory device which stores a plurality of batches of identification information identifying the plurality of living subjects, respectively; and judging means for judging the batch of identification information input through the input device is identical with each of batches of identification information stored in the memory device, and thereby identifying the each one living subject from the other living subjects.